Butadiene copolymers and method of preparing same



atented Sept. 11, 1945 au'rspmmz COPOLYMER8 sun salmon or rammamc sumDavid Craigg'iCuyahbga Falls, Ohio, assignor to No Drawing.

The BQF. Goodrich Company, New York, N. Y., I

incorporation New York Application October 16, 1840. Serial No. 881,433

Claims. (01. 260-74) This invention relates to new diene copolymers andto a method of preparing the same.

It is well known that aliphatic conjugated dienes such as butadiene,isoprene, dimethyl butadiene, piperylene and the like may be polymerizedto elastic vulcanizable masses of the general nature of rubber. It isalso well known that the properties of these diene synthetic rubberlikematerials may be improved appreciably by copohrmerizing the diene withone or more other compounds called comonomers which are capable offorming rubber-like copolymers with dienes. For example,a copolymer ofbutadiene and acrylonitrile possesses unusual oil resistance and issuperior to simple diene polymers in regard to elasticity and tensilestrength. Copolymerizing styrene with butadiene also produces asynthetic rubber of desirable properties. Other diene comonomers whichhave heretofore been proposed such as vinyl naphthalene, methyl gomethacrylate, vinylidene chloride and the like exert characteristiceflects on the properties of copolymers made by oopolymerizing dienestherewith.

I have now discovered that aryl oleflns which contain halogensubstituents in the aryl'nucleus such as p-chloro styrene are capable offorming copolymers with conjugated diene hydrocarbons and, whencopolymerized therewith, impart new and unexpected properties to thecopolymers Thus, I have found that copolymers of such dienes withhalogen substituted aryl oleflns are vastly superior to copolymers ofdienes with unsubstituted aryl olefins in regard to mechanicalproperties such as tensile strength and ultimate elongation, and,moreover, are appreciably resistant to the swelling action of mineraland vegetable oils, a property not present to any marked degree in thecopolymers of dienes with unsubstituted aryl olefins. These newcopolymers are also plastic, coherent and somewhat tacky and may readilybe worked on conventional rubber machinery. They also possess goodresistance to chemicals such as acids and alkalies, to heat and toaging.

Accordingly, this invention comprises copolymerizing conjugatedbutadiene hydrocarbons such as butadiene-1,3, isoprene, 2,3-dimethylbutadiene-LS, piperylene and the like, but preferably butadiene-L3, withhalogen substituted aryl oleiins. By the term halogen substituted aryloleiin is meant anaromatic compound which contains one or more halogenatoms attached to nuclear carbon atoms and which also contains apolymerizable oleflnic group a. o I also directly connected to a nuclearcarbon atom.

Such compounds may be represented structurally by the formula AIC=CH|wherein Ar is a halogen substituted aryl radical and R is hydrogen or analkyl group such as methyl or ethyl. Typical compounds in this classinclude p-chloro styrene. o-chloro styrene, pbromo styrene, o-bromostyrene. 1-vinyl'2,4 di chloro benzene, p-chioro alpha methyl styrene, 1vinyl 4 chloro naphthalene, 1 vinyl 2 chloro naphthalene and others. Thepreferred compounds are the chloro substituted vinyl benzenes and'vinylnaphthalenes such as p-chloro styrene and l-vinyl-i-chloro naphthalene.

These halogen substituted aryl olenns may be prepared in any of a numberof ways such as by the dehydrationof the appropriate aromatic alcohols,decarboxylation oi appropriate aromatic acids or from hydrocarbon orhalogenated hydrocarbon sources, the particular method of preparationbeing of not particular consequence in this invention. Mixtures ofvarious halogen substituted aryl olefins such as, for example, thetechnical mixtures of o and p chloro styrene may b; enployed instead ofthe pure materials, if des e It is also within thescope of thisinvention to polymerize mixtures including not only one or more dienesand one or more halogen substituted aryl oleiins but also other dienecomonomers such as acrylonitrile, styrene, methyl methacrylate,vinylidene chloride and the like since the multipolymers therebyobtained are often of particular value in that the desirable propertiesimparted to the polymer by the various comonomers are combined in asingle material.

It is generally true that, in any copolymeric system the specificproperties 01' the copolymerwill vary with the relative proportions ofthe comonomers and with the method and conditions of polymerization.This is also the case with the copolymers of dienes and halogensubstituted aryl olefins. For instance, the rubber-like properties of abutadiene; p chloro styrene copolymer such as elasticity andvulcanizability will be more pronounced when the copolymer contains atleast about 50% by weight, of butadiene. It is preferred, therefore,when arubber-like polymer is desired as the product to use from about 50to 80% by weight of the diene and from about 20 to 50% of the halogensubstituted aryl olefin or of a mixture of comonom'ers including ahalogen substituted aryl olefin. However, it is also within the purviewof this invention to employ mixtures of dienes with halogen substitutedaryl olefins in all proportions since copolymeric products having v pproperties of the copolymers or to modify the new and useful propertiesare obtained in each case.

Polymerization of the monomer mixture may be carried out in ahomogeneous system or in aqueous emulsion or by any other method offorming polymers. of polymerization is used, the monomer mixture isheated at a temperature between room temperature and about 100 0.,preferably. in presence of a substance capable of accelerating thereaction such as a peroxide, either with or without the presence of asolvent for the reaction. When polymerization is complete, which usuallyrequires several days by this method, the polymer is separated fromunreacted monomers and/or solvent if these are present, and themassivematerial is then processed in the usual manner.

The most eflicient and ,preferred method of polymerizing the monomermixtures of this invention, however, is to carry out the reaction in anaqueous emulsion; In this case the mixture of monomers is emulsifiedwith water by means of a suitable emulsifying agent, a polymerizationaccelerator or catalyst is preferably added together perhaps with othersubstances which activate the polymerization accelerator or whichotherwise influence the-polymerization in a desired manner, and theemulsion is allowed to polymerize by continuously agitating the same ata temperature of about -60 C. for a time sufiicientto complete thereaction, usually from about 15 to 150 hours. The copolym'er is obtainedin form of an aqueous dispersion resembling natural rubber latex, to

which an age resistor or antioxidant may be added, if desired, and whichmay then be utilized as such or coagulated by the same methods used tocoagulate rubber'latex, for example, by addition of acid, alcohol, orsalts or by a combination of these methods. The polymerization productsare washed and dried to produce a crude rubberlike material which'may beprocessed in substantially the samevmanner as natural rubber.

A wide range of materials may be used in the above process to bringabout emulsiflgation of the monomer mixture with water. Ordinary soapssuch as the sodium or potassium salts of saturated or unsaturated fattyacids, synthetic soap-like materials such as hymolal sulfates orsulfonates, aromatic sulfonates, and salts of high molecular weightaliphatic bases, for example, sodium lauryl sulfate, sodium naphthalenesulfonate, the hydrochloride of diethylaminoethyloleylamide andcetyltrimethylammonium methyl sulfate, and many other emulsifying agentsare operable in this invention. A very eifective emulsifying solution isone which contains a fatty acid such as myristic or palmitic acid'whichhas been from about 79 to 95% neutralized with alkali,

If the homogeneous method An equally wide range of materials isavailable for selection of the polymerization accelerator to be employedin the emulsion polymerization process. Catalysts soluble in' either theaqueous phase or the non-aqueous phase of the emulsion may be used.Among these are the peroxides such as hydrogen peroxide, diacylperoxides and benzoyl peroxide, per salts such as alkali metalperborates, persulfates and percarbonates, di azo compounds such asdiazo amino benzene and dipotassium diazcmethane disulfonate and othercompounds. Activators such as sodium pyrophosphate, sodium oxalate,acetanilide, urea, glycine, alanine, myristic acid and the like may beused in connection with the polymerization accelerator if desired. Insome instances it may be desirable to add other ingredients to improvethe course of the polymerization. By proper selection of the ingredientsgoing into the aqueous emulsionit is possible to speed up thepolymerization and to vary the properties of the polymerizationproducts.

In order to illustrate more clearly the manner in which this inventionmay be carried out, the following examples are cited but it is to beunderstood that many variations may be eflected without departing fromthe scope of the invention.

Example I Seventy parts by weight of butadiene and '30 parts by weightof p-chloro styrene are emulsified with 250 parts of a 2% aqueoussolution of myristic acid which has been neutralized with caustic soda.Ten parts of a 356% solution of hydrogen peroxide, 0.! part of sodiumpyrophosphate'and-OB' part of ferric pyrophosphate are added toaccelerate the polymerization. The emulsion is allowed to polymerize byagitation for 33 hours at a temperature of 40 C. Two parts of phenylbetanaphthylamine are added to the latex-like emulsion resulting fromthe polymerization and the emulsion is coagulated witha mixture ofalcohol and salt. The coagulum ob tained is a plastic, elastic, tackymaterial .quite similar inappearance to pale crepe rubber. The yield ofcopolymer is quantitative. The rubberlike copclymer may be masticatedwithout dimculty and may otherwise be processed in the same manner asnatural rubber. when compounded ina typical tire tread recipe withsulfur, carbon black, 'stearic acid, zinc oxide, softener andaccelerator, and vulcanized, excellent vulcanizates are obtained. Forexample, one such vulcanizate uhibits a tensile strength 0g 5100 lbs/sq.in. and an ultimate elongation of 730%, as compared with only a 4500lbs/sq. in. tensile and a 650% elongation of a similarly preparedvulcanizate from a butadiene styrene copolymer. This vulcanizate is alsoresistant to swelling by mineral oils and gasoline while the vulcanizatefrom a butadiene styrene copolymer does not possess this valuable'Emulsifying solution (2% aqueous acid, 85% neutralized); Diazoaminobenzene parts 16 .is polymerized at a temperature of 30 C. for 39 hours;Treatment or the synthetic latex as in "the'previous example produces an88% yield of myrlstic "a plastic copolymer. The copolymer is moderatelysoluble in benzene but is resistant to deterioration by dilute acids oralkalis or by corrosive chemicals. It is resistant to heat, sunlight andoxygen. Upon heating it becomes more plasare polymenzed as in Example I.A plastic oilresistant copolymer which may be worked easily on the millis obtained. When compounded and.

vulcanized exceptionally strong vulcanizates are produced.

As may readily be seen from the foregoing embodiments, copolymers, of'dienes and halogen substituted aryl oleflns are unexpectedly superiorto copolymers of dienes withunsubstituted aryl olefins since thesecopolymers possess improved tensile properties, are oil and chemicalresistant and yet are readily plastic and easily worked, s. combinationof properties which is ordinarily diilicult to obtain in a rubber-likematerial.

izing technique will obviously depend upon the particular vulcanizedarticle to be produced.

Other products 01' this invention which result from the copolymerizationof monomer mixtures wherein the halogen substituted aryl olefin ispresent. to the extent of about 60% or more are tougher, morethermoplastic, and are more dimcult to vulcanize. The rubber-likeproperties are Since, aslhas been mentioned above, the particularcharacteristics of the copolymer depend upon the relative proportions ofthe comonomers and the method and conditions oi. polymerization, thisinvention includes a variety ot products useful for a number ofpurposes. The products which are obtained by the copolymerization ofmonomer mixtures wherein the diene is present to the extent of 40-50% ormore by weight are generally useful as rubber substitutes.

They may be compounded with other materials such as other rubber-like orresinous products, pigments, plasticizers, vulcanizing ingredients,antioxidants, and the like and may be vulcanized as is natural rubber.Compounding and vulcannot so pronounced but the unexpected superiorityover the corresponding copolymers of unsubstituted aryl oleilns anddienes is still maintained. These products are purposes.

I claim:

1. The process which comprises polymerizing in aqueous emulsion amixture of monomers including a conjugated butadiene hydrocarbon, acompound of the formula wherein Ar is a chlorinated aryl radical and Ris a member of the class consisting of hydrogen and alkyl, andacryionitrile, said mixture contraining at least by weight of theconjugated butadiene hydrocarbon.

2. The process which comprises polymerizing in aqueous emulsion amixture of monomers including butadiene-l,3, p-chloro styrene. andacrylonitrile, said mixture containing at least 50% by weight ofbutadiene-L3.

3. The process which comprises polymerizing in aqueous emulsion amixture of monomers consisting of about 50% by weight of butadiene-1,3,

about 20% by weight or p-chloro styrene and about 30% by weight ofacrylonitrile.

4. An elastic vulcanizable copolymer of a conjugated butadienehydrocarbon, a compound 01 the formula Ar-C=CH:

wherein Ar is a chlorinated aryl radical and R is a member 01, the classconsisting oi. hydrogen and alkyl, and acrylonitrlle.

5. An elastic vclcaniz'qble copolymer oi butadiene-1,3, p-chloro styreneand acrylonitrile.

DAVID CRAIG.

also useful tor a number of

